Stereoselectivity and Stereospecificity of Cyclopropanation Reactions

with Stable (Phosphanyl)(silyl)carbenes. Ste´phanie Goumri-Magnet, Tsuyoshi Kato, Heinz Gornitzka, Antoine Baceiredo, and. Guy Bertrand*. Contributio...
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4464

J. Am. Chem. Soc. 2000, 122, 4464-4470

Stereoselectivity and Stereospecificity of Cyclopropanation Reactions with Stable (Phosphanyl)(silyl)carbenes Ste´ phanie Goumri-Magnet, Tsuyoshi Kato, Heinz Gornitzka, Antoine Baceiredo, and Guy Bertrand* Contribution from the Laboratoire d’He´ te´ rochimie Fondamentale et Applique´ e, UniVersite´ Paul Sabatier, 118 route de Narbonne, 31062 Toulouse Cedex 04, France ReceiVed December 16, 1999

Abstract: The stable (phosphanyl)(silyl)carbenes 1a,b react efficiently with various electron-poor alkenes [methyl acrylate, 3,3,4,4,5,5,6,6,6-nonafluorohex-1-ene, styrene, (Z)- and (E)-2-deuteriostyrene, (E)-t-BuOC(O)CHd CHC(O)OEt, and (E)-Me2NCOCHdCHCO2Me] giving the corresponding cyclopropanes in good yields. The stereochemical outcome was such that all monosubstituted alkenes gave exclusively the syn isomer (with respect to the phosphanyl group), and the addition of disubstituted alkenes was totally stereospecific. The high stereoselectivity observed was ascribed to a secondary orbital interaction (LUMOcarbene-HOMOalkene) similar to that explaining the endo-rule in Diels-Alder reactions.

Introduction

Scheme 1 paper,1

In a recent Krogh-Jespersen, Yan, and Moss wrote: “The addition of a carbene to an alkene with the formation of a cyclopropane is perhaps the most fundamental of cycloaddition reactions, as well as a basic component of the synthetic armamentarium.” Indeed, cyclopropanation reactions involving transient carbenes2 or even transition metal carbene complexes have been widely studied.3 Both singlet and triplet transient carbenes undergo cyclopropanation reactions, although with a totally different mechanism, which is apparent from the stereochemistry of the reaction: with singlet carbenes the stereochemistry about the original carbon-carbon double bond is maintained, while with triplet carbenes the stereochemical information is lost.4 Additionally, for all types of carbene, including transition metal-carbene complexes, intermolecular cyclopropanation usually occurred in poor to moderate diastereoselectivity (syn- versus anti-attack).5 To date, two types of stable singlet carbene are known:6 the phosphanylcarbenes I and the aminocarbenes II. For derivatives of type II, no cyclopropanation reactions have been reported, most probably because of the strong donation of the amino (1) Krogh-Jespersen, K.; Yan, S.; Moss, R. A. J. Am. Chem. Soc. 1999, 121, 6269. (2) (a) Moss, R. A. Acc. Chem. Res. 1989, 22, 15. (b) Minkin, V. I.; Ya Simkin, B.; Glukhovtsev, M. N. Russ. Chem. ReV. 1989, 58, 1067. (c) Regitz, M. Carbene (Carbenoide); Methoden der Organische Chemie (Houben-Weyl); Thieme Verlag: Stuttgart, 1989; Vol. E19b, Parts 1 and 2. (d) de Meijere, A. Carbocyclic Three-Membered Ring Compounds; Methoden der Organische Chemie (Houben-Weyl); Thieme Verlag: Stuttgart, 1996; Vol. E17a. (3) (a) Brookhart, M.; Studabaker, W. B. Chem. ReV. 1987, 87, 411. (b) Harvey, D. F.; Sigano, D. M. Chem. ReV. 1996, 96, 271. (c) Fru¨hauf, H. W. Chem. ReV. 1997, 97, 523. (4) (a) Skell, P. S.; Garner, A. Y. J. Am. Chem. Soc. 1956, 78, 3409 and 5430. (b) Skell, P. S.; Woodworth, R. C. J. Am. Chem. Soc. 1956, 78, 4496 and 6427. (c) Skell, P. S. Tetrahedron 1985, 41, 1427. (d) Gaspar, P. P.; Hammond, G. S. In Carbenes; Moss, R. A., Jones, M., Jr., Eds., WileyInterscience: New York, 1973; Vol. II, p 153. (5) ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds; Pergamon Press: New York, 1991; Vol. 4. (6) For reviews on stable singlet carbenes see: (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G. Chem. ReV. 2000, 100, 39. (b) Herrmann, W. A.; Ko¨cher, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2162. (c) Bourissou, D.; Bertrand, G. AdV. Organomet. Chem. 1999, 44, 175.

substituent, which makes the vacant orbital too high in energy.7 For example, the 1,2,4-triazol-5-ylidene IIa reacts with diethyl fumarate and diethyl maleate to give methylenetriazoline derivatives and not the corresponding cyclopropanes.8 In contrast, we have already shown that the (phosphanyl)(silyl)carbenes 1a,b react with dimethyl fumarate with retention of the stereochemistry about the double bond to give the corresponding trans-cyclopropane.9 However, since 1 does not react with dimethyl maleate no conclusion could be drawn on the stereospecificity of the reaction (Scheme 1). The difference in reactivity between cis and trans alkenes toward carbenes has (7) This is well illustrated by the structure of the radical anion IIa•obtained by reduction of the corresponding stable carbene IIa. According to ESR spectroscopy and ab initio calculations, the additional electron is not located at the carbene carbon atom but delocalized into the PhCN fragment: Enders, D.; Breuer, K.; Raabe, G.; Simonet, J.; Ghanimi, A.; Stegmann, H. B.; Teles, J. H. Tetrahedron Lett. 1997, 38, 2833. (8) Enders, D.; Breuer, K.; Raabe, G.; Runsink, J.; Teles, J. H.; Melder, J. P.; Ebel, K.; Brode, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1021.

10.1021/ja994408b CCC: $19.00 © 2000 American Chemical Society Published on Web 04/22/2000

Reactions of the Stable (Phosphanyl)(silyl)carbenes

J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4465

Table 1. Crystallographic Data for Cyclopropanes 2a, 6b, 7a, 7b, 8a, and 15a 2a formula formula wt cryst system, space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z d(calcd), Mg/m3 absorp coeff, mm-1 no of total reflcns no of unique reflcns R1 (I > 2σ(I)) wR2a (all data) (∆/F)max [eÅ-3] a

C20H43N2O2SiP 402.62 monoclinic, P21/c 15.147(8) 9.852(4) 18.554(8) 114.04(2) 2529(2) 4 1.058 0.171 22045 3403 0.0523 0.1392 0.204 and -0.163

6b C36H61N2SiP(C7H8)0.5 627 triclinic, P1h 10.013(2) 10.937(2) 17.832(3) 79.51(2) 76.75(2) 89.38(2) 1868.1(6) 2 1.115 0.134 10001 5065 0.0385 0.1021 0.190 and -0.248

7a

7b

8a

15a C23H48N3O3SiPS 505.76 orthorhombic, Pna21 10.233(1) 17.265(2) 16.354(2) 90 90 90 2889.3(6) 4 1.163 0.236 23935 4580 0.0395 0.0913 0.175 and -0.132

C24H45N2SiPS 452.74 monoclinic, P21/n 10.293(2) 13.027(2) 19.551(3)

C36H61N2SiPS 612.99 monoclinic, P21/c 12.552(1) 16.173(2) 17.548(1)

C26H53N2O4SiP 516.76 monoclinic, P21/c 36.818(5) 9.5963(12) 18.765(2)

94.96(2)

97.72(1)

104.749(6)

2611.7(8) 4 1.151 0.244 20109 3875 0.0331 0.0825 0.250 and -0.264

3530.0(6) 4 1.153 0.198 28238 5328 0.0354 0.0875 0.235 and -0.365

6411.5(15) 8 1.071 0.152 14359 5699 0.994 0.2832 0.443 and 0.401

wR2 ) {[Σw(Fo2 - Fc2)2]/[Σw(Fo2)2]}1/2.

Scheme 2

Figure 1. Solid-state structure of cyclopropane 2a.

already been noted by Moss et al. with the methoxy(phenyl)carbene.10 On the other hand, we have reported that 1a reacted with methyl acrylate to give the corresponding cyclopropane as only one diastereomer 2a.9 However, the total selectivity of the reaction was quite surprising, and the structure only based on questionable NMR data. Here, we report a detailed study of the reactions of the stable (phosphanyl)(silyl)carbenes 1a and 1b with various electronpoor alkenes, focusing particularly on their diastereoselectivity (syn- versus anti-attack) and diastereospecificity. Results We first reproduced the synthesis of the phosphanylcyclopropane 2a9 by addition of methyl acrylate to the carbene 1a (Scheme 1).11a The total syn-selectivity (with respect to the phosphanyl group), according to NMR spectroscopy, was confirmed by a single-crystal X-ray diffraction study (Figure 1, Table 1). According to multinuclear NMR spectroscopy, the (phosphanyl)(silyl)carbene 1a quantitatively reacts with 3,3,4,4,5,5,6,6,6nonafluorohex-1-ene, affording the cyclopropane 3a as a single diastereomer (Scheme 2). The total syn-selectivity was suggested (9) (a) Igau, A.; Baceiredo, A.; Trinquier, G.; Bertrand, G. Angew. Chem., Int. Ed. Engl. 1989, 28, 621. (b) Gillette, G. R.; Igau, A.; Baceiredo, A.; Bertrand, G. New J. Chem. 1991, 15, 393. (10) Moss, R. A.; Shen, S.; Hadel, L. M.; Kmiecik-Lawrynowicz, G.; Wlostowska, J.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1987, 109, 4341. (11) (a) Igau, A.; Gru¨tzmacher, H.; Baceiredo, A.; Bertrand, G. J. Am. Chem. Soc. 1988, 110, 6463. (b) Alcaraz, G.; Reed, R.; Baceiredo, A.; Bertrand, G. J. Chem. Soc., Chem. Commun. 1993, 1354.

by the large 4JPF coupling constant (178.5 Hz), which cannot readily be explained without involving a through space coupling.12 Treatment of a thf solution of 3a with a stoichiometric amount of hydrated tetrabutylammonium fluoride gave rise to the syn-cyclopropane 4a (95% yield) which also showed a large 4J PF coupling constant (145.9 Hz). The phosphanylcarbene 1c is unavailable because of its instability.11a Its diazo precursor 5a is stable toward dinitrogen elimination on heating at 40 °C for 3 h. Interestingly, under the same experimental conditions, but in the presence of the perfluoroalkyl-substituted alkene, cyclopropane 4′a was obtained in 95% yield (Scheme 2). The anti-configuration was apparent from the 31P and 19F NMR spectra: no JPF coupling constants were observed. The reaction of carbene 1a with styrene was monitored by 31P NMR spectroscopy. After 30 min at room temperature, the reaction was over, and two new signals at +73 and +61 ppm in a 90/10 ratio were observed, arguing for the presence of two diastereomers. A white solid was obtained after treatment with elemental sulfur, and purification by column chromatography. Although one single spot was apparent on the TLC, two signals (+93 and +86 ppm; 60/40 ratio) were observed in the 31P NMR spectrum of a CDCl3 solution of the solid. The 1H and 13C NMR spectra confirmed the presence of two species, but the similarities of their spectroscopic data (Table 2) were surprising for two diastereomers. Slow evaporation of a pentane solution of the solid gave single crystals suitable for an X-ray diffraction study. The molecular structure of the molecule is depicted in (12) Spectroscopic Methods in Organic Chemistry; Hesse, M., Meier, H., Zeeh, B., Eds; Georg Thieme Verlag: Stuttgart, 1997; pp 202-204.

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Goumri-Magnet et al.

Table 2. Selected 1H NMR Resonance Values and Coupling Constants for Cyclopropanes 7a, 10a, 12a, and 15a

7a 10a 12a 15a

δ 31P (ppm)

δ Ha (2JHH, 3J(HH)trans, 3JPH)

δ Hb (2JHH, 3J(HH)cis, 3JPH)

δ Hc (2J(HH)cis, 3J(HH)trans, 3JPH)

85.9 major 93.2 minor 85.9 major 93.0 minor 85.9 major 93.1 minor 90.8

1.73 (4.2, 7.3, 19.6) 2.43 (3.9, 8.6, 20.6)

not observed

2.53 (7.8, 7.3, 17.6) 2.69 (8.0, 8.6, 17.2) 2.52 (7.8, -, 17.6) 2.69 (8.5, -, 16.8) 2.50 (-, 7.3, 18.6) 2.68 (-, 7.9, 16.8) 3.35 (-, 5.4, 16.4)

not observed 1.71 (-, 7.3, 19.4) 2.42 (-, 8.0, 22.4) 2.9 (-, 5.4, 18.8)

Figure 2. Solid-state structure of cyclopropane 6b.

Scheme 3

Figure 2. In the unit cell, the two enantiomers corresponding to the syn-cyclopropane 7a were observed, suggesting that a diastereoselective crystallization occurred. However, the room temperature 31P NMR spectrum of a CDCl3 solution of the single crystal showed the two signals previously observed at +93 and +86 ppm in the same 60/40 ratio! On cooling this solution to 240 K only the signal at +86 ppm was observed, while heating at T > 363 K led to the decomposition of the product. These results as a whole strongly suggest that a stereoselective syncyclopropanation occurred leading to 6a, which exists as two rotamers in a slow equilibrium (Scheme 3). Very similar results were observed using the [bis(dicyclohexylamino)phosphanyl](silyl)carbene 1b.11b However, in this case, single crystals of both the phosphanyl-substituted cyclopropane 6b and thioxophosphoranyl-substituted cyclopropane 7b, suitable for analysis by X-ray diffraction, were obtained (Figures 3 and 4). These studies confirmed the exclusive formation of the syn-cyclopropanes 6b and 7b and that unexpected isomerization does not occur in the sulfuration process (Scheme 3). The phosphanylcarbene 1a also reacts with the unsymmetrically substituted olefin (E)-t-BuOC(O)CHdCHC(O)OEt to give a 9/1 mixture of cyclopropanes 8a and 8′a. The major isomer 8a was isolated by selective recrystallization as colorless crystals in 40% yield. An X-ray diffraction study (Figure 5) unambiguously established the anti-position of the tert-butyl group with respect to the phosphanyl group. Addition at room temperature of 3 equiv of (Z)- and (E)-2deuteriostyrene to the carbene 1a afforded the cyclopropanes 9a and 11a, respectively. Addition of elemental sulfur, followed by column chromatography gave rise to the thioxophosphoranyl

Figure 3. Solid-state structure of cyclopropane 7a.

Figure 4. Solid-state structure of cyclopropane 7b.

Figure 5. Solid-state structure of cyclopropane 8a.

analogues 10a and 12a in 95 and 96% yield, respectively (Scheme 5). Again, in both cases two rotamers were observed. The relative configuration of the three stereogenic centers of 10a and 12a was determined based on the 1H NMR spectra of cyclopropanes 7a, 10a, and 12a (Table 2). By comparing the spectra of 7a and 10a, it is clear that Ha has been substituted by a deuterium atom: its signal is not present and the JHaHc

Reactions of the Stable (Phosphanyl)(silyl)carbenes

J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4467

Scheme 4

Scheme 5

Figure 6. Solid-state structure of cyclopropane 15a.

we obtained exclusively the isomer featuring the amido and phosphanyl substituents syn to one another. Discussion

Table 3. Philicity of Phosphino(silyl)carbene 1b toward Styrenes

X

X

kX/kH

CH3O H F CF3

H H H H

0.88 1 1.7 7

Scheme 6

coupling constant is not observed. In the spectrum of 12a, the signals of both Ha and Hc are present, but no coupling constants with Hb are observed. In both cases, no trace of other isomers was detected. Interestingly, photolysis at 300 nm of the diazo precursor 13a in the presence of (Z)-2-deuteriostyrene led after sulfuration to a 9/1 mixture of cyclopropanes 10a and 12a (Scheme 5). However, we have checked that irradiation of (Z)-2-deuteriostyrene under the same experimental conditions (during the same period of time) gave a 9/1 mixture of (Z)- and (E)-2deuteriostyrene. Competitive reactions of phosphinocarbene 1b with various para-substituted styrenes have been carried out, and the results are summarized in Table 3. The carbene 1a also readily reacts at room temperature with (E)-Me2NCOCHdCHCO2Me to give the corresponding cyclopropane 14a, in near quantitative yield. Treatment with elemental sulfur gave the corresponding thioxophosphoranyl derivative 15a (45% yield) (Scheme 6), which was fully characterized including by an X-ray diffraction study (Figure 6). Interestingly,

The total syn-stereoselectivity (with respect to the phosphanyl group) observed in the reaction of the carbenes 1 with methyl acrylate, styrene, and the perfluoroalkene was quite surprising (Schemes 1, 2, and 3). Indeed, looking at the molecular structures (Figures 1-4), it is hard to believe that steric factors could govern the observed selectivity since the bis(amino)phosphanyl group appears to be roughly as sterically demanding as the trimethylsilyl group. The definitive proof that the phosphanyl group is in fact more sterically demanding than the trimethylsilyl group is given by the results observed with the alkene substituted by the ethyl and tert-butyl ester groups: the major isomer 8a features the bulkier ester group anti with respect to the phosphanyl group. Since the syn-selectivity observed with the carbenes 1 is not due to steric factors, the obvious other possibility is to invoke orbital-controlled reactions. Thus, it was first necessary to check that the cyclopropanation reactions were concerted (or at least quasiconcerted). Although the total stereospecificity observed in the reaction of 1a with (Z)- and (E)-2-deuteriostyrene is not a definitive proof for the concerted nature of the cyclopropanation reactions, this is a strong argument13 (Scheme 5). Before drawing a reasonable hypothesis to explain the observed syn-selectivity, it was necessary to check whether carbenes 1 are nucleo- or electrophilic in character.2a Indeed, although their nucleophilic character appears from the calculations,14 we recently reported that 1b reacted with phosphines to give the correspnding phosphorus ylides,15 which suggests that 1b features an accessible vacant orbital and therefore could behave as an electrophile. The results observed with different styrene derivatives (Table 3) leave no doubt that the carbenes 1 are the nucleophilic partners in the cycloaddition reaction with olefins. For example, using the same set of styrene derivatives, but the electrophilic H-C-CO2Et carbene generated by coppercatalyzed decomposition of the corresponding ethyl diazoacetate, (13) The stereochemical results are most compatible with concerted addition of 1a to styrene, in accord with typical singlet carbene behavior, and with the lack of theoretical prohibition of concerted nucleophilic carbene-olefin [1+2] cycloadditions. However, there is no spin-inversion barrier to rapid closure of a 1,3-dipole, so that a two-step singlet carbene addition is not as certain to occur nonstereospecifically as in a triplet carbene addition, which proceeds via a triplet 1,3-diradical. Moss, R. A.; Huselton, J. K. J. Chem. Soc., Chem. Commun. 1976, 950. (14) (a) Nguyen, M. T.; McGinn, M. A.; Hegarty, A. F. Inorg. Chem. 1986, 25, 2185. (b) Hoffmann, M. R.; Kuhler, K. J. Chem. Phys. 1991, 94, 8029. (c) Dixon, D. A.; Dobbs, K. B.; Arduengo, A. J., III; Bertrand, G. J. Am. Chem. Soc. 1991, 113, 8782. (d) Nyulaszi, L.; Szieberth, D.; Reffy, J.; Veszpremi, T. J. Mol. Struct. (THEOCHEM) 1998, 453, 91. (15) Goumri-Magnet, S.; Polishchuk, O.; Gornitzka, H.; Marsden, C. J.; Baceiredo, A.; Bertrand, G. Angew. Chem., Int. Ed. Engl. 1999, 38, 3727.

4468 J. Am. Chem. Soc., Vol. 122, No. 18, 2000

Goumri-Magnet et al. Scheme 7

Figure 7. Schematic representation of the cycloaddition of phosphino(silyl)carbene to acroleine.

somerization of the alkene, while using the stable carbene 1a, only 9a is formed.

the reverse relative rate of cyclopropanation has been observed.16 It is important to note that in the latter case a range of syn/anti isomers from 1:1 to 1:15 was obtained.16 At this point, it seems clear that the (phosphanyl)(silyl)carbenes have to be compared with methoxymethylcarbene17 for which the nucleophilic character is strongly expressed but its electrophilicity not totally suppressed (as observed for the dimethoxycarbene).18 Therefore, in the transition state, the more dominant orbital interaction is between the HOMOcarbene and the LUMOalkene (Figure 7a), but this set of orbitals does not explain the observed syn-selectivity. However, in the course of computational and experimental19 work on the addition of carbenes to alkenes the significance of a second pair of orbital interactions in the addition geometry has been pointed out. Thus, our hypothesis was that the secondary orbital interaction LUMOcarbene-HOMOalkene (Figure 7b) should explain the selectivity observed. Due to donation of the phosphorus lone pair, the LUMOcarbene has some π*(PC) character and shows significant bonding overlap between the phosphorus center and the alkene substituent, as indicated schematically in Figure 7b. In other words, like the endo selectivity in the Diels-Alder reaction,20 the high stereoselectivity observed could be rationalized on the basis of favorable “secondary orbital interactions”. The effectiveness of the secondary orbital interactions on the selectivity of cyclopropanation reactions is demonstrated by the exclusive formation of 14a (Scheme 6). Not surprisingly, simple Hu¨ckel calculations show that the highest coefficient of the HOMO of the alkene is located at the amido group, and thus despite the smaller steric demand of the ester group, the amido substituent lies syn with respect to the phosphanyl group. On the other hand, the synthetic importance of having stable carbenes is nicely illustrated by the reaction of the phosphanyldiazomethane 5a with the perfluoro-substituted alkene, which leads to the anti-cyclopropane 4′a, while desilylation of 3a affords the syn-cyclopropane 4a (Scheme 2). Since in the absence of olefin the diazo derivative 5a is stable toward nitrogen elimination, it is quite clear that the formation of 4′a does not involve the carbene 1c but results from a [3+2]cycloaddition process giving the transient pyrazoline 16a, which undergoes a classical nitrogen elimination21 (Scheme 7). Note also that when the carbene 1a is generated under irradiation in the presence of (Z)-2-deuteriostyrene, a mixture of cis- and trans-cyclopropanes 9a and 11a is obtained due to the photoi-

Conclusion

(16) Diaz-Requejo, M. M.; Pe´rez, P. J.; Brookhart, M.; Templeton, J. L. Organometallics 1997, 16, 4399. (17) Sheridan, R. S.; Moss, R. A.; Wilk, B. K.; Shen, S.; Wlostowski, M.; Kesselmayer, M. A.; Subramanian, R.; Kmiecik-Lawrynowicz, G.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1988, 110, 7563. (18) Dunn, J. A.; Pezacki, J. P.; McGlinchey, M. J.; Warkentin, J. J. Org. Chem. 1999, 64, 4344 and references therein. (19) (a) Keating, A. E.; Merrigan, S. R.; Singleton, D. A.; Houk, K. N. J. Am. Chem. Soc. 1999, 121, 3933. (b) Rondan, N. G.; Houk, K. N.; Moss, R. A. J. Am. Chem. Soc. 1980, 102, 1770. (20) “Endo rule”: Woodward, R. B.; Hoffmann, R. The conserVation of Orbital Symmetry; Verlag Chemie: Weinheim, 1971. (21) Regitz, M.; Heydt, H. In 1,3-Dipolar Cycloaddition Chemistry; Padwa, A., Ed.; Wiley: New York, 1984; Vol. 1, pp 393-558.

These results present convincing evidence for the concerted nature of cyclopropanation reaction and therefore the genuine singlet carbene nature of stable phosphanylsilylcarbenes. To date, the observed diastereoselectivity (where present) of cyclopropanation reactions involving transient nucleophilic singlet carbenes has been rationalized by steric factors.22 Here, we demonstrate that the diastereoselectivity is due to secondorder orbital interactions, in a manner analogous to the wellknown endo rule for the Diels-Alder reaction. These reactions allow the diastereoselective synthesis of various cyclopropanes with simultaneous control of two or even three stereogenic centers. The enantioselective version of this reaction is under active investigation. Experimental Section All manipulations were performed under an inert atmosphere of argon using standard Schlenk techniques. Dry, oxygen-free solvents were employed. 1H, 13C, 19F, and 31P NMR spectra were recorded on Brucker AC80, AC200, WM250, or AMX400 spectrometers. 1H and 13C chemical shifts are reported in ppm relative to Me Si as external 4 standard. 31P and 19F NMR downfield chemical shifts are expressed with a positive sign, in ppm, relative to external 85% H3PO4 and CF3CO2H, respectively. Infrared spectra were recorded on a Perkin-Elmer FT-IR Spectrometer 1725 X. Mass spectra were obtained on a Ribermag R10 10E instrument. Preparation of the Carbenes 1a,b. In a typical experiment, phosphanyl(silyl)carbenes 1a,b were obtained by irradiation (300 nm, 8 h) of a pentane solution (3 mL) of the corresponding phosphanyl(silyl)diazomethane11 (0.30 mmol). According to 31P NMR spectroscopy the reactions were quantitative and the carbenes 1a,b were used without any further purification. General Procedure for Cycloaddition Reactions with the Carbenes 1a,b. To a pentane solution (3 mL) of the carbene 1 (0.3 mmol) was added at room temperature 3 equiv of alkene. The resulting mixture was stirred at room temperature and the progress of the reaction was monitored by 31P NMR spectroscopy. After the reaction was complete (1-3 h), volatile components were removed under reduced pressure, and the phosphanylcyclopropanes were analyzed without any further purification. Treatment of a thf solution of phosphanylcyclopropanes with an excess of elemental sulfur gave the corresponding thioxophosphoranyl derivatives, which were purified as indicated for each compound by column chromatography on silica gel. 3a: Yellow oil. 31P{1H} NMR (CDCl3) δ 78.2 (d, 4JPF ) 178.5 Hz); 19F{1H} NMR (CDCl : δ -51.3 and -46.0 (m, CF -CF -CF -), 3 3 2 2 -34.2 (dd, 2JFF ) 265.1 Hz, 2JPF ) 178.5 Hz, CF2-CH), -25.9 (s, CF2-CH), -5.0 (t, 3JFF ) 9.0 Hz, CF3). 4a: To a thf solution (3 mL) of the cyclopropane 3a (0.1 g, 0.18 mmol) was added at room temperature 1 equiv of Bu4NF (0.05 g, 0.18 mmol). The reaction was monitored by 31P NMR spectroscopy, and the cyclopropane 4a was obtained after 3 h in near-quantitative yield (according to NMR spectroscopy). 31P{1H} NMR (CDCl3) δ 44.1 (d, 4J ) 145.9 Hz); 19F{1H} NMR (CDCl ) δ -49.7 and -47.1 (m, CF PF 3 3 CF2-CF2-), -43.1 (dd, 2JFF ) 268.1 Hz, 2JPF ) 145.9 Hz, CF2CH), -28.7 (s, CF2-CH), -5.1 (m, CF3). (22) See, for example: Brahms, D. L. S.; Dailey, W. P. Chem. ReV. 1996, 96, 1585.

Reactions of the Stable (Phosphanyl)(silyl)carbenes 4′a: A pentane solution (3 mL) of the diazo compound 5a11a (0.1 g, 0.37 mmol) and nonafluoro-1-hexen (193 µL, 1.11 mmol) was heated at 40 °C. The reaction was monitored by 31P NMR spectroscopy, and the cyclopropane 4′a was obtained after 2 h in near-quantitative yield (according to the NMR spectroscopy). 31P{1H} NMR (CDCl3) δ 50.6; 19 F{1H} NMR (CDCl3) δ -50.1 and -46.2 (m, CF3-CF2-CF2-), -35.4 (m, CF2-CH), -5.0 (t, 3JFF ) 8.7 Hz, CF3). 6a: 31P{1H} NMR (C6D6) δ 76.6 and +61.0 ppm (2 rotamers, 90/ 10 ratio). 7a: (pentane/ether, 98/2, RF ) 0.6). (0.12 g; 90%). Mp 163-164 °C; 31P{1H} NMR (C6D6) δ 85.9 and 93.2 (2 rotamers, 60/40); 1H NMR (C6D6) major rotamer δ 0.33 (s, 9 H, SiCH3), 0.50 (d, 6 H, 3JHH ) 7.0 Hz, CHCH3), 1.13 (d, 6 H, 3JHH ) 6.8 Hz, CHCH3), 1.29-1.50 (m, 12 H, CHCH3), 1.73 (ddd, 2JHH ) 4.2 Hz, 3JHH ) 7.3 Hz, 3JPH ) 19.6 Hz, 1 H, CH2), 2.53 (td, 3JHH ) 7.8 Hz, 3JPH ) 17.6 Hz, 1 H, CH), 3.54-4.11 (m, 4 H, CHCH3), 7.17-7.61 (m, 5 H, Harom), one of the CH2 protons was not observed, minor rotamer δ 0.30 (s, 9 H, SiCH3), 1.27-1.51 (m, 24 H, CHCH3), 2.43 (ddd, 2JHH ) 3.9 Hz, 3JHH ) 8.6 Hz, 3JPH ) 20.6 Hz, 1 H, CH2), 2.69 (td, 3JHH ) 8.0 Hz, 3JPH ) 17.2 Hz, 1 H, CH), 3.54-4.11 (m, 4 H, CHCH3), 7.17-7.61 (m, 5 H, Harom), one of the CH2 protons was not observed; 13C{1H} NMR (C6D6)major rotamer δ 0.6 (s, SiCH3), 15.1 (d, 2JPC ) 5.1 Hz, CH2), 21.0 (d, 1JPC ) 91.6 Hz, PC), 23.7 (d, 3JPC ) 6.9 Hz, CHCH3), 24.0 (s, CHCH3), 25.5 (s, CHCH3), 26.6 (d, 3JPC ) 1.2 Hz, CHCH3), 29.6 (d, 2J 2 4 PC ) 5.9 Hz, CH), 48.2 (d, JPC ) 6.0 Hz, CHN), 126.9 (d, JPC ) 17.4 Hz, Co), 128.2 (s, Cp), 130.8 (d, 4JPC ) 8.5 Hz, Cm), 137.5 (s, Ci). Anal. Calcd for C24H45N2SiPS: C, 63.67; H, 10.02; N, 6.19. Found: C, 64.01; H, 10.15; N, 5.98. 6b: Yellow crystals from a pentane solution at -20 °C (0.16 g, 95%). Mp 210-211 °C; 31P{1H} NMR (CDCl3) δ 76.4 and +67.4 ppm (2 rotamers, 95/5 ratio). Anal. Calcd for C36H61N2SiP: C, 70.43; H, 10.58; N, 4.82. Found: C, 70.23; H, 10.45, N, 4.65. 7b (hexane/ether, 95/5, RF ) 0.8): Pale yellow crystals were obtained by slow evaporation of a pentane solution (0.16 g; 90%). Mp 196197 °C; 31P{1H} NMR (CDCl3) δ 84.4. Anal. Calcd for C36H61N2SiPS: C, 70.54; H, 10.03; N, 4.57. Found: C, 70.14; H, 9.83, N, 4.71. 8a and 8′a: 31P{1H} NMR (CD2Cl2, 293 K) δ 89.7 very large. By cooling the sample, two rotamers were observed for each compound, 31P{1H} NMR (CD Cl , 223 K) δ 96.5 and 88.0 (major isomer 8a), 2 2 87.8 and 87.0 (minor isomer 8′a). At 193 K, only one rotamer was detected for each isomer,31P{1H} NMR (CD2Cl2, 193 K) δ 88.0 (8a),and 87.8 (8′a) (90/10 ratio). The major isomer 8a precipitated from a pentane solution at -50 °C as colorless crystals (0.04 g; 40%). Mp 147-148 °C; 1H NMR (CD2Cl2, 193 K) δ 0.23 (s, 9 H, SiCH3), 1.22 (d, 12 H, 3JHH ) 6.7 Hz, CHCH3), 1.23 (d, 6 H, 3JHH ) 6.7 Hz, CHCH3), 1.29 (d, 3 H, 3JHH ) 7.2 Hz, OCH2CH3), 1.43 (s, 9H, tBu), 2.56 (tlike, 3J 3 3 3 HH ) JPH ) 6.1 Hz, 1 H, CHring), 2.73 (dd, 1 H, JHH ) 6.0 Hz, JPH ) 12.2 Hz, CHring), 3.50 (m, 4 H, CHCH3), 4.00 (dq, 1 H, 3JHH ) 7.2 Hz, 2JHH ) 10.8 Hz, OCH2CH3), 4.22 (dq, 1 H, 3JHH ) 7.2 Hz, 2JHH ) 10.8 Hz, OCH2CH3); 13C{1H} NMR (CD2Cl2, 193 K) δ 0.9 (d, 3JPC ) 9.6 Hz, SiCH3), 14.5 (s, OCH2CH3), 24.5 (d, 3JPC ) 17.5 Hz, CHCH3), 26.9 (d, 3JPC ) 15.3 Hz, CHCH3), 28.1 (s, OC(CH3)3), 34.8 (d, 2JPC ) 2.3 Hz, CHring), 35.7 (d, 2JPC ) 9.0 Hz, CHring), 38.1 (d, 1JPC ) 91.8 Hz, PCSi), 45.1 (d, 2JPC ) 37.9 Hz, CHN), 51.1 (d, 2JPC ) 10.0 Hz, CHN), 61.4 (s, OCH2CH3), 81.0 (s, OC(CH3)3), 172.8 (d, 3JPC ) 5.4 Hz, CO), 174.8 (d, 3JPC ) 8.0 Hz, CO). Anal. Calcd for C26H53N2O4PSi: C, 60.43; H, 10.34; N, 5.42; Found: C, 60.22; H, 10.28; N, 5.36. 9a: 31P{1H} NMR (C6D6) δ 73.5. 10a (pentane/ether, 98/2, RF ) 0.6): Colorless crystals of 10a were obtained by slow evaporation of a dichloromethane solution (0.13 g; 95%). Mp 161-162 °C; 31P{1H} NMR (C7D8) δ 85.9 and 93.0 (2 rotamers, 60/40); 1H NMR (C7D8) major rotamer δ 0.51 (s, 9 H, SiCH3), 1.11 (d, 12 H, 3JHH ) 7.0 Hz, CHCH3), 1.13 (d, 12 H, 3JHH ) 7.0 Hz, CHCH3), 2.52 (dd, 3JHH ) 7.8 Hz, 3JPH ) 17.6 Hz, 1 H, CH), the proton of CDH was not observed, 4.32 (m, 4 H, CHCH3), 7.227.71 (m, 5 H, Harom), minor rotamer δ 2.69 (dd, 3JHH ) 8.5 Hz, 3JPH ) 16.8 Hz, 1 H, CH), the proton of CDH was not observed. 11a: 31P{1H} NMR (C6D6) δ 73.5. 12a (pentane/ether, 98/2, RF ) 0.5): Colorless crystals of 12a were obtained by slow evaporation of a dichloromethane solution (0.13 g;

J. Am. Chem. Soc., Vol. 122, No. 18, 2000 4469 95%). Mp 163-164 °C; 31P{1H} NMR (CDCl3) δ 85.9 and 93.1 (2 rotamers 60/40); 1H NMR (CDCl3) major rotamer δ 0.25 (s, 9 H, SiCH3), 1.07-1.54 (m, 24 H, CHCH3), 1.71 (dd, 3JHH ) 7.3 Hz, 3JPH ) 19.4 Hz, 1 H, CHD), 2.50 (dd, 3JHH ) 7.3 Hz, 3JPH ) 18.6 Hz, 1 H, CH), 3.85 (m, 4 H, CHCH3), 7.19-7.80 (m, 5 H, Harom), minor rotamer 2.42 (dd, 3JHH ) 8.0 Hz, 3JPH ) 22.4 Hz, 1 H, CHD), 2.68 (dd, 3JHH ) 7.9 Hz, 3JPH ) 16.8 Hz, 1 H, CH). Reaction of the Diazo 13a in the Presence of (Z)-2-Deuteriostyrene. A pentane solution (3 mL) of phosphanyl(silyl) diazomethane (13a, 0.10 g, 0.30 mmol) and 3 equiv of (Z)-2-deuteriostyrene (0.09 g, 0.90 mmol) was irradiated at 300 nm for 18 h. According to 31P NMR spectroscopy the reaction was quantitative (δ 73.5). Treatment of the solution mixture with an excess of elemental sulfur gave the thioxophosphoranyl derivatives 10a and 12a in a 90/10 ratio (according to 1H NMR spectroscopy). 14a: Yellow oil. 31P{1H} NMR (C7D8) δ 94.0; 1H NMR (C7D8) δ 0.65 (d, 4JPH ) 1.0 Hz, 9 H, SiCH3), 1.45 (d, 6 H, 3JHH ) 6.8 Hz, CHCH3), 1.49 (d, 6 H, 3JHH ) 6.8 Hz, CHCH3), 1.55 (d, 6 H, 3JHH ) 6.8 Hz, CHCH3), 1.71 (d, 6 H, 3JHH ) 6.8 Hz, CHCH3), 2.81 (s, 3 H, CH3N), 2.84 (s, 3 H, CH3N), 3.00 (dd, 3JHH ) 6.4 Hz, 3JPH ) 4.8 Hz, 1 H, CHring), 3.50 (dd, 3JHH ) 6.4 Hz, 3JPH ) 11.4 Hz, 1 H, CHring), 3.59 (s, 3 H, CH3O), 3.80 (sept d, 3JHH ) 6.8 Hz, 3JPH ) 9.0 Hz, 4 H, CHCH3); 13C{1H} NMR (C7D8) δ 1.9 (d, 3JPC ) 8.8 Hz, SiCH3), 24.8 (d, 3JPC ) 4.9 Hz, CHCH3), 24.9 (d, 3JPC ) 3.5 Hz, CHCH3), 34.6 (d, 2J 2 PC ) 3.4 Hz, CHring), 35.8 (s, CH3N), 35.9 (d, JPC ) 7.2 Hz, CHring), 1 36.7 (d, JPC ) 100.0 Hz, PCSi), 37.5 (s, CH3N), 51.6 (s, CH3O), 52.4 (d, 2JPC ) 15.9 Hz, CHN), 170.8 (d, 3JPC ) 6.5 Hz, CO), 174.1 (d, 3JPC ) 5.2 Hz, CO). 15a: White crystals obtained by slow evaporation of a ether solution (0.06 g; 45%). Mp 191-192 °C dec; 31P{1H} NMR (C7D8) δ 90.8; 1H NMR (C7D8) δ 0.76 (s, 9 H, SiCH3), 1.20-2.17 (m, 24 H, CHCH3), 2.90 (dd, 3JHH ) 5.4 Hz, 3JPH ) 18.8 Hz, 1 H, CHring), 2.89 (s, 3 H, CH3N), 3.07 (s, 3 H, CH3N), 3.34 (s, 3 H, CH3O), 3.35 (dd, 3JHH ) 5.4 Hz, 3JPH ) 16.4 Hz, 1 H, CHring), 4.23, 4.44, 4.50, and 4.63 (m, 4 H, CHCH3); 13C{1H} NMR (C7D8) δ 4.3 (s, SiCH3), 23.0 (s, CHCH3), 23.8 (s, CHCH3), 25.6 (s, CHCH3), 25.8 (s, CHCH3), 25.9 (d, 3JPC ) 4.2 Hz, CHCH3), 29.2 (d, 2JPC ) 3.1 Hz, CHring), 33.6 (d, 2JPC ) 2.7 Hz, CHring), 34.9 (d, 1JPC ) 79.7 Hz, PCSi), 35.6 (s, CH3N), 39.3 (s, CH3N), 53.1 (s, CH3O), 47.3 (s, CHN), 47.8 (d, 2JPC ) 7.4 Hz, CHN), 50.1 (s, CHN), 51.7 (d, 2JPC ) 8.2 Hz, CHN), 166.2 (d, 3JPC ) 6.6 Hz, CO), 171.9 (d, 3JPC ) 4.4 Hz, CO). Anal. Calcd for C23H48N3O3SiPS: C, 54.62; H, 9.57; N, 8.31. Found: C, 54.83; H, 9.70; N, 8.41. Competition Experiments (p-X-C6H4-CHdCH2 vs C6H4-CHd CH2) Using Carbene 1b. In a typical experiment, 1 equiv of styrene and 1 equvi of para-substituted-styrene (X ) CH3O, F, CF3) was added at room temperature to a pentane solution (3 mL) of phosphanyl(silyl)carbene 1b. When the reaction had reached completion (1-3 h), volatile components were removed in vacuo, and the ratios of the resulting cyclopropanes were determined by 1H NMR spectroscopy without any further purification. The phosphanylcyclopropanes resulting from the reaction of 1b with the different para-substituted-styrenes were independently prepared. X ) CH3O: 31P{1H} NMR (CDCl3) δ 76.7 and +68.5 (2 rotamers, 90/10 ratio); 1H NMR (CDCl3) δ 0.11 (s, 9 H, SiCH3), 0.53-1.64 (m, 41 H, CH2 and CHring), 2.51-2.89 (m, 6 H, CHN and CHring), 3.64 (s, 3 H, CH3O), 6.54-7.17 (m, 5 H, CHarom). X ) F: 31P{1H} NMR (CDCl3) δ 76.2 and +67.7 (2 rotamers, 90/10 ratio); 1H NMR (CDCl3) δ 0.12 (s, 9 H, SiCH3), 0.81-1.63 (m, 41 H, CH2 and CHring), 2.52-3.04 (m, 6 H, CHN and CHring), 6.73-7.15 (m, 5 H, CHarom). X ) CF3: 31P{1H} NMR (CDCl3) δ 76.3 and +67.9 (2 rotamers, 90/10ratio); 1H NMR (CDCl3) δ 0.14 (s, 9 H, SiCH3), 0.43-1.99 (m, 41 H, CH2 and CHring), 2.56-2.96 (m, 6 H, CHN and CHring), 7.24-7.39 (m, 5 H, CHarom). X-ray Crystallographic Studies of Compounds 2a, 6b, 7a, 7b, 8a, and 15a. Crystal data for all structures are presented in Table 1. Data for 6b, 7a, 7b, and 15a were collected at low temperatures on a Stoe-IPDS diffractometer and data for 2a and 8a were collected at room temperature on a Bruker-CCD with Mo KR (λ ) 0.71073 Å). The structures were solved by direct methods by means of SHELXS-9723 (23) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467.

4470 J. Am. Chem. Soc., Vol. 122, No. 18, 2000 and refined with all data on F2 by means of SHELXL-97.24 All nonhydrogen atoms were refined anisotropically. The hydrogen atoms of the molecules were geometrically idealized and refined using a riding model. Refinement of an inversion twin parameter25 [x ) -0.16(9); x ) 0 for the correct absolute structure and x ) +1 for the inverted structure] confirmed the absolute structure of 15a. (24) Sheldrick, G. M., SHELXL-97, Program for Crystal Structure Refinement, Universitat Gottingen, 1997. (25) Flack, H. D. Acta Crystallogr. Sect. A 1983, 39, 876.

Goumri-Magnet et al. Acknowledgment. Thanks are due to the French Embassy in Tokyo for a grant (to T.K.) and to the CNRS for financial support of this work. Supporting Information Available: X-ray crystallographic data for compounds 2a, 6b, 7a, 7b, 8a, and 15a (PDF). This material is available free of charge via the Internet at http://pubs.acs.org. JA994408B